This application is based upon and claims the benefits of priority from the prior Japanese Patent Application No. 2002-150971, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an electrical junction box, and more particularly, to an electrical junction box mounted on a motor vehicle for interconnecting wire harnesses laid inside the vehicle.
2. Description of the Related Art
An electrical junction box mounted on a motor vehicle has numerous electrical connection terminals densely populated in a small space thereof. It is therefore necessary to prevent the connection terminals from being connected and thus short-circuited by water which has entered the electrical junction box during a rainfall or the washing of the vehicle or by small drops of water which are formed inside the junction box by condensation.
Unexamined Japanese Utility Model Publication No. 5-70123 discloses an electrical junction box containing a laminated wiring board formed by stacking busbars and insulating substrates one upon another. This publication proposes a structure for preventing a grounding busbar for a grounded circuit, which is situated on the lowermost layer of the laminated wiring board, from being short-circuited due to bridging of water collected on the bottom of a lower case of the electrical junction box. Specifically, the lowermost insulating substrate is provided with ribs. The ribs are formed on a lower surface of the lowermost insulating substrate and defines grooves for arranging the grounding busbar and the other busbars thereof according to a predetermined layout. On the other hand, water bridge prevention ribs are arranged at the bottom of the lower case so as to face the ribs of the lowermost insulating substrate of the laminated wiring board, to completely isolate the grounding busbar from the other busbars by means of the ribs of the lowermost insulating substrate and the water bridge prevention ribs and thereby prevent the grounding busbar from being connected to the other busbars due to bridging of water.
With this short circuit prevention structure, however, water collects on the bottom of the lower case and possibly corrodes the busbars.
Unexamined Japanese Utility Model Publication No. 7-16528 discloses an electrical junction box containing an insulating substrate with busbars. Each busbars has tab protruding from the busbar. The electrical junction box has outlet holes formed through the bottom of a lower case thereof to allow the tabs of busbars to be extended outside. Each outlet hole is in the form of a cross so as to permit the tab to pass therethrough as well as to drain water flowing down to the bottom of the lower case.
Even with this structure, water present between the busbars and the insulating substrate or water formed on the busbars by condensation cannot be drained out and possibly corrodes the busbars.
Unexamined Japanese Patent Publication No. 10-51932 also discloses an electrical junction box containing a laminated wiring board formed by stacking insulating substrates with busbars one upon another. Each insulating substrate has a drain hole formed in a central portion thereof and a drainpipe protruding downward from the drain hole. The drainpipe is contact with the lower insulating substrate and connected to the drain hole thereof. Further, a water shutoff rib with a constant height is formed on each insulating substrate and surrounds the drain hole thereof and the drainpipe of the upper insulating substrate. Thus, part of water that has entered the electrical junction box and is present on each insulating substrate flows over the water shutoff rib and is guided through a gap between the drain pipe of the upper insulating substrate and the upper surface of the insulating substrate, the drain holes and drainpipe toward the bottom of a lower case of the junction box. The remaining part of water, which failed to flow over the water shutoff ribs, flows back toward the outer peripheral edges of the insulating substrate and is guided to the bottom of the lower case through gaps between the inner wall surface of the lower case and the outer peripheral edges of the individual substrates.
Since the busbars are arranged on the insulating substrates, however, water which failed to flow over the water shutoff ribs is obstructed when flowing toward the outer peripheral edges of the insulating substrates through small spaces between the busbars and the insulating substrates located directly above. It is therefore difficult to completely drain water from the individual layers of the laminated wiring board, possibly causing a situation where the busbars are corroded.
An object of the present invention is to provide an electrical junction box for a motor vehicle which can prevent electrical connection terminals arranged therein from being short-circuited by water that has entered or is formed inside the electrical junction box and also can prevent the connection terminals from being corroded by water remaining in the junction box.
To achieve the object, the present invention provides an electrical junction box comprising: a lower case containing a wiring board with basbars such that the wiring substrate stands upright; an upper case combined with the lower case; a plurality of upper connection terminals extended from the wiring board and vertically penetrating through an upper terminal supporting member attached to the wiring board to be supported by the upper terminal supporting member, the upper connection terminals extending upward and fitted into the upper case; a plurality of lower connection terminals extended from the wiring board and vertically penetrating through a lower terminal supporting member attached to the wiring substrate to be supported by the lower terminal supporting member, the lower connection terminals extending downward and penetrating through the lower case; and short circuit prevention means for preventing the upper connection terminals and/or the lower connection terminals from being connected and thus short-circuited by water that has entered the electrical junction box.
The above and other objects, features and advantages of the present invention will become apparent from the following description.